The new knowledge of polymorphonuclear neutrophil (PMN) signaling in relation to effector responses, and their transcriptional and cell-cell interactive capabilities, affords the opportunity to expand investigations of PMN adaptive and inappropriate roles in burn/ trauma and sepsis injury conditions. This study will focus on PMN signaling, cytokine expression and cell-cell interactions during burn injury complicated by Enterococcus faecalis infection. The latter organism has been increasingly recognized as a pathogen causing serious morbidity in intensive care patients. Our recent studies have shown that inoculation of E. faecalis in burned rats produces hemodynamic instability and mortality not seen with the individual burn or E. faecalis challenges. Our previous and preliminary studies have shown burn injury alone causes upregulation of PMNs' signaling, contributing to their enhanced oxidant production, protease release and adhesion to endothelial cells. We hypothesize that PMNs' tissue damaging actions, via oxidant production, protease release, and cell-cell interactions, are exacerbated to produce the animal morbidity and mortality with combined burn and E. faecalis injuries. The investigation of mechanisms of PM"s inappropriate portentiated responses will be carried out in a rat model of 30 percent total body surface area burn plus an intraabdominal inoculation of Enterococcus faecalis using two strains of the organism, one expressing and one not expressing the AS (Aggregation Substance) protein which has been implicated in enhancing E. faecalis virulence. Specific aim 1 will establish linkage between potentiated oxidant production, elastase release, adhesion to endothelial cells, and altered apoptosis of PMNs to ithe signaling pathways involving protein tyrosine kinases (PTK), phophtidylinositol 3-kinase (PI-3K), and mitogen- lactivated protein kinases (MAPK), Erk and p38. The approach in this aim would be to determine if in vivo administrations of signaling blocker agents to the injured animals result in an attenuatiodprevention of the potentiated PMN effector response. Specific aim 2 will assess if PMN transmigration across endothelial and epithelial barriers are altered and whether such alterations are related to PMN release of elastase causing damage to the endothelial and/or epithelial adherense junctions by hydrolyzing the junction protein cadherin. Specific aim 3 will evaluate PMN expression of chemokines, CINC, MIP-2 and MIPl a, and proinflammatory cytokines, IL-1beta, IL-6, and their autocrine/paracrine potentiation of PMN chemotaxis and anti-apoptotic behavior. Specific aim 4 is to evaluate the relevance of potentiated effector responses by PMNs in producing damage to structural/functional integrity of intestine, and their relevance to hemodynamic instability and mortality in the burned-E. faecalis infected animals. The proposed studies will enhance our understanding of the role of potentiated PMN effector responses in causing host morbidity and mortality in burn injury complicated by enterococcal infections.